Functional Polymer Nanocomposite Materials from Microfibrillated Cellulose

Abstract

In line with recent environmental policies, increased attention has been paid to the development of bio-based nanocomposite materials for several industrial applications, such as automotive, construction, packaging or medical applications. Thus, much effort has been devoted to the use of natural fibers in composite materials as an alternative to conventional inorganic fillers, traditionally used to reinforce thermoplastic matrices (i.e., glass fibers, aramid or carbon fibers, for instance).(Eichhorn, 2006; Pandey, et al., 2005) Hence, natural fibers present very attractive properties such as low cost, renewability, biodegradability and low density.(Bledzki & Gassan, 1999; Samir, et al., 2005) Cellulose is the most abundant biopolymer on earth, and is present in natural fibers such as wood, cotton or hemp, as well as in a wide variety of living species, such as animals, plants and bacteria. This linear polymer is composed of β-1,4 linked glucopyranose units, with polymer chains associated by hydrogen bonds forming bundles of fibrils, also called microfibrillar aggregates, where highly ordered regions (i.e., crystalline phases) alternate with disordered domains (i.e., amorphous phases).(Samir, Alloin & Dufresne, 2005) In the last decades, the production of cellulose nanofibers from different sources has gained a tremendous success. Hence, apart from the already mentioned advantages related to natural fibers, cellulosic nanoelements also possess very high strength and stiffness, therefore making them excellent reinforcing agents for nanocomposites. As will be discussed later in detail, two main types of cellulose nanofibers can be produced: the Cellulose nanowhiskers (CNW) and Microfibrillated cellulose (MFC). These natural fillers differ from their size and crystallinity, but the highest aspect ratios are usually found for MFC. In the past decade, the EMPA Wood Laboratory has acquired a strong experience in the production, functionalization and use of MFC for a wide range of applications, including adhesives, packaging or medical applications. Consequently, this book chapter will specifically address the elaboration of functional nanocomposite materials using MFC as reinforcing agent. A first section will present the production and properties of MFC. In a second section, the chemical modification of MFC will be presented, therefore highlighting the possibility to tailor the surface polarity of the cellulosic fillers. Finally, a third section will address the elaboration of nanocomposite materials from unmodified and functionalized MFC.